It is known to provide a material handling system that includes vacuum cups or the like that are adapted to be moved into engagement with an object, such as a substantially flat object or panel or the like, and to lift and move the object to a desired location. Such vacuum cups or suction cups may be moved into engagement with the object, and a vacuum source may be actuated to create a partial vacuum between the object and the cup such that the object is retained to the cup as it is transported to the targeted area. An example of such a vacuum cup is disclosed in U.S. Pat. No. 4,662,668, issued May 5, 1987 to Hufford for MATERIAL HANDLING SENSOR DEVICE AND METHOD, which is hereby incorporated herein by reference in its entirety.
The vacuum at the cup may be provided by a venturi nozzle, whereby pressurized air is supplied or provided to a venturi nozzle at the cup and the air forced through the venturi nozzle creates a vacuum at the cup to seal the cup to the object surface. The venturi nozzle has an inlet port connected to the air supply and an exit port through which the air is blown. The internal cavity defined by the vacuum cup and object is in fluid communication with the venturi nozzle so that air is drawn out of the cavity as the air is blown through the venturi nozzle. When the air supply is deactivated, the vacuum within the cup cavity may slowly dissipate through the port that connects the vacuum cup cavity to the venturi nozzle and through the exit port of the venturi nozzle. Thus, there may be a delay between when the air supply is deactivated and when the vacuum dissipates a sufficient amount to readily release the vacuum cup from the object.
Typically, venturi vacuum generators use compressed air to generate vacuum via Bernoulli's principle and the Venturi effect, and thus, the air needs to be passing through the venturi nozzle the entire time that the vacuum is needed at the vacuum cup. In an effort to save compressed air and the associated cost of producing compressed air, it has been proposed to use a combination of an electronic vacuum sensor or electronic vacuum sensing switch and vacuum check valve to shut off the air supply and maintain vacuum. When the full vacuum is reached, the vacuum sensing switch senses the vacuum level and sends an electronic control signal to the valve to shut off the supply of air to the venturi nozzle while the check valve holds or substantially maintains the vacuum level in the vacuum cup. Because the vacuum may bleed off slowly (such as due to leakage at the vacuum cup seal), the electronic vacuum sensing switch will sense a lower vacuum level and turn the air supply back on to restore full vacuum, and then shut off the air supply when the vacuum level is again achieved. This configuration requires an electrical connection as well as a second air line to provide air to the vacuum cup to release the part from the vacuum cup.